1. Field of the Invention
The invention deals with a device fitted on vehicles for monitoring the air pressure in the vehicle's tires.
2. Discussion of the Prior Art
In known devices for monitoring the air pressure in the tires of a vehicle, pressure sensors are arranged in the wheels and each pressure sensor is connected with a transmitter. Here, an antenna is positioned in the vicinity of each wheel and the antennas are connected with a common receiving and evaluating circuitry. The transmitters provided in the wheels are not synchronized with each other. Therefore, it is possible that the signal strings coming from the various wheels overlap at the input side of the receiving and evaluating circuitry, thereby preventing unambiguous evaluation. This difficulty has previously been resolved where the disclosed device for monitoring the tire pressure is provided with a pressure sensor and a transmitter, which are integrated in the valve cap of each wheel in the form of an electronic assembly. In order to obtain the measured tire pressure by remote scanning, a preferably portable remote control unit equipped with a transmitter/receiver combination is provided. This unit is deployed in the vicinity of the selected tire to activate and scan the electronic assembly. In this case the tire pressure can be monitored only from time to time when the vehicle is standing still, but not when it is moving. However, for the purpose of scanning the electronic assembly provided in the valve cap. It is known to provide transmitting and receiving devices which are not contained in a portable remote control unit but are fixed to the chassis of the vehicle in the vicinity of the wheel, as well as providing display devices on the dashboard. This is an expensive solution, since the signals which are emitted by the transmitter located in a particular wheel and which contain the air pressure determined by the pressure sensor, are each transmitted wirelessly to a separate transmitting and receiving device assigned to each wheel.
A similar device is disclosed has been disclosed where the pressure sensor and the transmitter are not located in the valve cap but at the valve spud.
It is also known to provide an assembly consisting of a pressure sensor and a transmitter at the valve spud of an air tire, whereby to each transmitter in a particular tire valve is assigned a tuned-in receiver in the vicinity of the vehicle's wheel.